The present invention pertains to override systems for valves. A typical example of the type of valve assembly to which the present invention may be applied in a rotary valve assembly, such as a butterfly valve, which includes a valve body or housing defining a flowway, a valve element rotatably mounted in the flowway for movement between a closed position, blocking the flowway, and an open position, permitting passage therethrough, and a valve stem connected to the valve element and extending outwardly therefrom. Typically, an actuator is connected to the valve element for rotating it along with the attached valve element to open and close the valve. The invention can also be applied to other types of valves, such as gate valves or other reciprocating type valves, particularly if the movement of the valve element and attached valve stem, although ultimately reciprocatory in nature, may be effected by a rotary output member of the valve actuator, e.g. through a screw and nut type connection.
Where the valve actuator is an automatic type, such as a pneumatic, hydraulic or electric actuator, it is conventional to provide manual override means which may be used to manually open or close the valve, as when the actuator fails, is in process of being repaired or serviced, etc. Prior override systems have been fraught with a number of problems.
Some of these problems stem from the interconnection of the actuator with the remainder of the system. In such systems, the primary or automatic actuator was not adequately deactivated during operation of the manual override. For example, with actuators of the pneumatic or hydraulic type, it was typically necessary, in operating the manual override, not only to provide enough force to operate the valve per se, but in addition, to overcome the resistance of pressurized fluid trapped within a pneumatic or hydraulic cylinder of the actuator.
In other cases, the use of the override would be occasioned by circumstances also resulting in loss of power to the actuator. For example, if the actuator were pneumatic, power to the actuator might be temporarily lost during repair work on the compressor for the pneumatic fluid. Sudden return of power at the time of completion of such repair would cause sudden and/or rapid movements of the actuator and valve. This in turn could result in injury to an operator who might be attempting to use the override at the time the air pressure or power returned.
Still other problems with typical prior art valve/ actuator/override systems are results of the nature and structure of the override mechanisms themselves. Such conventional override mechanisms typically have gear systems in which the gears are constantly engaged, and in which the override is rendered operative or inoperative by engaging and disengaging connections between two rotary shafts, one on the override, and the other on the valve element or actuator. These conventional override mechanisms were large, e.g. due to the need for room to move keys in and out of engagement with the various shafts. Their large size not only made them difficult to mount and operate, but also heavy. The size and weight problems were even further increased in that, due to the nature of the structure and operation of these devices, if the parts were not made relatively large and heavy, they would fail in use.